Cystic fibrosis is a common lethal genetic disease that is caused by different mutations in the Cystic Fibrosis Transmembrane Regulator (CFTR) gene and is classically associated with progressive lung disease, exocrine pancreatic insufficiency, and elevated sweat Cl- levels. Some mutations are associated with unusual clinical phenotypes, including mild lung disease, pancreatic sufficiency, and/or normal sweat Cl-. The mechanisms by which normal CFTR and CFTR with mutations associated with mild or severe disease may evaluated effectively in in vitro systems that maintain differentiated properties comparable to those of the native tissues. The overall objective of the proposed project is to develop epithelial cell lines from airway epithelia and sweat gland epithelia of patients with specific CFTR mutations, and to identify and partially characterize cell lines that retain differentiated phenotypic properties reflective of the in vivo state. Subjects with homozygous rare CFTR mutations that are associated with mild disease have agreed to participate in this study. Airway and sweat gland epithelial cells from small biopsy specimens will be cultured and infected with a retrovirus carrying papilloma which extend the life of cultured cells but have small effects on phenotypic properties. Cells with increased growth capability will be selected, propagated, and screened for retention of a well-differentiated phenotype. Ion transport capabilities and other characteristics of the best lines will be evaluated, and the cells will be supplied to collaborating investigators for additional studies designed to elucidate the mechanisms by which certain CFTR mutations confer mild disease.